Holding device

Abstract

To suppress leakage of an inert gas from a gas passage.SOLUTION: A holding device that holds an object includes a first ceramic layer formed of ceramic, a plate-shaped second ceramic layer disposed on the first ceramic layer and formed of ceramic, an intermediate layer disposed between the first ceramic layer and the second ceramic layer, and a gas flow path penetrating the first ceramic layer, the intermediate layer, and the second ceramic layer, wherein the intermediate layer has an outer peripheral portion located on an outer side and a central portion located on an inner side in a direction orthogonal to a stacking direction of the first ceramic layer, the intermediate layer, and the second ceramic layer, the porosity of the outer peripheral portion is smaller than the porosity of the central portion.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a retaining device. [Background technology]

[0002] Holding devices such as electrostatic chucks that attract and hold semiconductor wafers are known (see, for example, Patent Document 1). In the field of electrostatic chucks described in Patent Document 1, in order to make the surface temperature of the wafer attracted and held by the electrostatic chuck uniform, an inert gas (e.g., helium gas) may be supplied into a minute gap between the wafer and the holding surface of the electrostatic chuck that holds the wafer. A gas flow path for supplying this inert gas is formed inside the electrostatic chuck. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-67767 Summary of the Invention [Problem to be solved by the invention]

[0004] In electrostatic chucks, which supply inert gas to the minute gap between the wafer and the holding surface, if the ceramic layer that forms the holding surface contains many pores, there is a risk of the inert gas leaking through the pores. Furthermore, the chuck electrode that electrostatically attracts the wafer is often made slightly smaller than the holding surface. Therefore, the temperature tends to rise more easily toward the periphery of the wafer held by the electrostatic chuck. If the inert gas leaks, the entire wafer cannot be cooled, and there is a risk of temperature variations occurring across the wafer.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and has an object to suppress leakage of inert gas from a gas flow path. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, there is provided a holding device for holding an object, the holding device including: a first ceramic layer made of ceramic; a plate-shaped second ceramic layer made of ceramic and disposed on the first ceramic layer; an intermediate layer disposed between the first ceramic layer and the second ceramic layer; and a gas flow path passing through the first ceramic layer, the intermediate layer, and the second ceramic layer, the intermediate layer having an outer peripheral portion located outside and a central portion located inside in a direction perpendicular to a stacking direction of the first ceramic layer, the intermediate layer, and the second ceramic layer, the porosity of the outer peripheral portion being smaller than the porosity of the central portion.

[0008] According to this configuration, the porosity of the intermediate layer is smaller in the outer periphery than in the center. That is, the outer periphery of the intermediate layer is formed more densely than the center. This prevents the inert gas from leaking to the outside through the intermediate layer when an inert gas or the like is supplied between the surface holding the object and the held object through the gas flow path. As a result, the inert gas supplied to the gas flow path is sufficiently delivered to the object placement surface, and the inert gas homogenizes the temperature within the surface of the object. Furthermore, although the center of the intermediate layer is compressed by atmospheric pressure, the porosity of the center is higher than that of the outer periphery, allowing the center to function as a stress relief layer that relieves stress. In particular, the closer the gas flow path is to the center, the more the leakage of the inert gas is suppressed, and the better the center functions as a stress relief layer.

[0009] (2) In the holding device of the above aspect, the thickness of the intermediate layer in the stacking direction may be 50 micrometers (μm) or less. According to this configuration, the thickness of the intermediate layer is small, 50 μm or less, so that the inert gas supplied to the gas flow passage is prevented from leaking to the outside through the intermediate layer.

[0010] (3) The holding device of the above form may further include a plate-shaped electrode arranged inside the first ceramic layer, and the thickness of the portion of the first ceramic layer between the electrode and the intermediate layer in the stacking direction may be smaller than the thickness of the second ceramic layer and larger than the thickness of the intermediate layer. With this configuration, the thickness of the second ceramic layer that holds the object is increased, improving the dechucking performance of the object. On the other hand, increasing the thickness of the second ceramic layer brings the intermediate layer closer to the inlet of the gas flow path, which may increase the risk of inert gas leakage. However, with this configuration, the porosity of the outer periphery of the intermediate layer is smaller than the porosity of the center, suppressing inert gas leakage and improving the dechucking performance of the object.

[0011] (4) In the holding device of the above aspect, the porosity of the second ceramic layer may be smaller than the porosity of the first ceramic layer. With this configuration, the porosity of the second ceramic layer, where the wafer holding surface is exposed, is smaller than the porosity of the first ceramic layer, thereby improving the voltage resistance of the holding device and the particle resistance of the second ceramic layer.

[0012] (5) In the holding device of the above aspect, the intermediate layer may be made of ceramic. According to this configuration, in addition to the first and second ceramic layers, the intermediate layer is also made of ceramic, which makes the entire holding device less susceptible to deterioration due to plasma irradiation.

[0013] (6) In the holding device of the above aspect, the first ceramic layer, the intermediate layer, and the second ceramic layer may each have the same main component. With this configuration, the first ceramic layer, the intermediate layer, and the second ceramic layer are formed from the same material as the main component, and because the materials forming these three layers have similar compositions, the difference in thermal expansion when the three layers are sintered together is suppressed.

[0014] The present invention can be realized in various forms, for example, a holding device, an electrostatic chuck, a system including these, a method for manufacturing a holding device, a method for manufacturing an electrostatic chuck, etc. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic perspective view of a holding device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic cross-sectional view of a holding device. [Figure 3] 10 is a flowchart of a method for manufacturing the holding device of the present embodiment. [Figure 4] FIG. 10 is an explanatory diagram of a press jig used in the joining step. [Figure 5] FIG. 2 is an explanatory diagram of a cross-sectional photograph of a first ceramic layer, an intermediate layer, and a second ceramic layer. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Embodiment> FIG. 1 is a schematic perspective view of a holding device 1 according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the holding device 1. FIG. 1 shows the holding device 1 and a wafer (object) W that is attracted and held by the holding device 1. The holding device 1 of this embodiment is an electrostatic chuck that attracts and holds the wafer W using electrostatic attraction. The holding device 1 is used, for example, in semiconductor wafer transport, exposure, film formation processes such as CVD (Chemical Vapor Deposition), and microfabrication such as shaping, etching, and dicing.

[0017] The holding device 1 shown in FIG. 1 is formed by stacking a first ceramic layer 10, an intermediate layer 30, and a second ceramic layer 20 in this order from bottom to top along the stacking direction (Z-axis direction). The Cartesian coordinate system CS shown in FIG. 1 is composed of a Z-axis parallel to the stacking direction and X- and Y-axes perpendicular to each other in a plane direction perpendicular to the Z-axis. The Cartesian coordinate system CS shown in FIG. 1 corresponds to the Cartesian coordinate system CS shown in FIG. 2 and subsequent figures. In FIGS. 1 and 2, the arrangement of each part is shown schematically, and the dimensional ratios of each part are not accurately shown.

[0018] As shown in FIG. 2, the holding device 1 includes a first ceramic layer 10 made of ceramic, a disk-shaped chuck electrode (electrode) 40 arranged inside the first ceramic layer 10, a plate-shaped second ceramic layer 20 made of ceramic, an intermediate layer 30 arranged between the first ceramic layer 10 and the second ceramic layer 20, and a gas flow path 50.

[0019] The first ceramic layer 10 of this embodiment is formed of ceramics containing aluminum oxide (alumina, Al2O3) as its main component. In this specification, the term "main component" refers to a component with a content of 90 wt% or more. As shown in FIGS. 1 and 2, the first ceramic layer 10 is formed by combining two disk-shaped portions, an upper portion 11 and a lower portion 12, with different areas along the stacking direction. As shown in FIG. 2, the upper portion 11 is located on the positive side of the Z-axis in the first ceramic layer 10 and is in contact with the intermediate layer 30. In the planar direction, the area of ​​the upper portion 11 is smaller than the area of ​​the lower portion 12.

[0020] The chuck electrode 40 of this embodiment is made of a conductive material (e.g., tungsten, molybdenum, etc.). As shown in FIG. 2, the chuck electrode 40 is embedded in the upper portion 11 of the first ceramic layer 10. The chuck electrode 40 has a disk shape extending in the planar direction about a central axis OL1. The chuck electrode 40 generates an electrostatic attraction force (attraction force) when power is supplied from a power source (not shown). The electrostatic attraction force attracts and fixes the wafer W to the mounting surface 21 of the second ceramic layer 20.

[0021] 2, the lower portion 12 of the first ceramic layer 10 includes a heater electrode 13 and a power line 14. The heater electrode 13 has, for example, a substantially spiral pattern extending in the surface direction and is made of a conductive material (for example, tungsten, molybdenum, platinum, etc.). Power is supplied to the heater electrode 13 via the power line 14 connected to a power source (not shown), and the heater electrode 13 generates heat to heat the wafer W held on the mounting surface 21. The surface of the lower portion 12 on the negative side of the Z axis is joined to, for example, a metal base or the like.

[0022] As shown in FIG. 2 , the gas flow path 50 includes a communication hole 51 formed in the lower portion 12 of the second ceramic layer 20, a tunnel 53 connected to the communication hole 51, and a through hole 52 connected to the tunnel 53. The tunnel 53 is an annular cavity formed along the circumferential direction of a central axis OL1 parallel to the stacking direction. The communication hole 51 is composed of a hole extending in the stacking direction and a hole extending in the surface direction. The communication hole 51 connects the negative Z-axis side of the lower portion 12, i.e., the outside of the first ceramic layer 10, to the tunnel 53. The through hole 52 is a hole extending in the stacking direction. The through hole 52 connects to the tunnel 53 on the negative Z-axis side and opens at the mounting surface 21 of the second ceramic layer 20 in the positive Z-axis direction. Through hole 52 penetrates first ceramic layer 10, chuck electrode 40, intermediate layer 30, and second ceramic layer 20 from tunnel 53 to mounting surface 21. Therefore, in other words, gas flow path 50 penetrates first ceramic layer 10, intermediate layer 30, and second ceramic layer 20. Note that in this specification, "penetrating in the stacking direction" does not only mean penetrating only through a path along the stacking direction, but also includes penetrating through a path along the stacking direction or a path intersecting the stacking direction, as in communication hole 51.

[0023] The second ceramic layer 20 has a disk shape in the planar direction with the same area as the upper portion 11 of the first ceramic layer 10. In this embodiment, the second ceramic layer 20 is formed from the same material as the first ceramic layer 10, that is, ceramics containing alumina as the main component.

[0024] The intermediate layer 30 has a disk shape in the planar direction with the same area as the upper portion 11 of the first ceramic layer 10 and the second ceramic layer 20. The intermediate layer 30 is formed of a sintered body of a material in which a binder and a solvent are added to alumina powder. The main component of the intermediate layer 30 is ceramic alumina. Examples of binders that can be used include Ethocel resin and butyral resin. Examples of solvents that can be used include butyl carbitol, butyl carbitol acetate, terpineol, and Texanol. In this embodiment, the retaining device 1 is manufactured by disposing the intermediate layer 30, which functions as an adhesive, between the first ceramic layer 10 and the second ceramic layer 20 and sintering it.

[0025] The intermediate layer 30 of this embodiment has an outer peripheral portion located on the outside and a central portion located on the inside in the surface direction. The porosity of the outer peripheral portion of the intermediate layer 30 is formed to be smaller than the porosity of the central portion. The central portion refers to the 50% toward the center in the surface direction (50% toward the center in the radial direction). The outer peripheral portion refers to the outer 10% in the surface direction (the portion other than the 90% toward the center in the radial direction). In this case, the remaining 40% in the surface direction is a portion that does not belong to either the central portion or the outer peripheral portion.

[0026] The diameter in the planar direction of the upper portion 11 of the first ceramic layer 10, the intermediate layer 30, and the second ceramic layer 20 may be, for example, about 50 mm to 500 mm, and is usually 200 mm to 350 mm. The diameter in the planar direction of the lower portion 12 of the first ceramic layer 10 may be, for example, about 220 mm to 550 mm, and is usually 220 mm to 350 mm.

[0027] The first ceramic layer 10 is formed so that the thickness t10u of the first ceramic layer 10 along the stacking direction from the surface of the chuck electrode 40 on the positive side of the Z axis to the intermediate layer 30 is 1 μm or more and 150 μm or less. The intermediate layer 30 is formed so that the thickness t30 of the intermediate layer 30 along the stacking direction is 50 μm or less. The second ceramic layer 20 is formed so that the thickness t20 of the second ceramic layer 20 along the stacking direction is 150 μm or more and 350 μm or less. In particular, in this embodiment, the holding device 1 is formed so that the thickness t10u of the first ceramic layer 10 is smaller than the thickness t20 of the second ceramic layer 20 and larger than the thickness t30 of the intermediate layer 30.

[0028] FIG. 3 is a flowchart of a method for manufacturing the holding device 1 of this embodiment. In the manufacturing flow shown in FIG. 3, first, a fired ceramic body that will become the first ceramic layer 10 and the second ceramic layer 20 is prepared (step S1). The fired ceramic body is formed by stacking a plurality of alumina green sheets. A fired body for the first ceramic layer 10 and a fired body for the second ceramic layer 20 are prepared separately. In the process of step S1, tunnels 53, communication holes 51, and portions of through holes 52 are formed in the fired body for the first ceramic layer 10. Note that the portions of the through holes 52 that will be formed in the second ceramic layer 20 and the intermediate layer 30 are formed in the process of step S5, which will be described later.

[0029] The fired ceramic bodies are polished to a predetermined thickness (step S2). In the polishing, the fired bodies of the first ceramic layer 10 and the fired bodies of the second ceramic layer 20 are polished to a predetermined thickness. Furthermore, the polishing is performed to make each fired body flat. Processing to match the radial dimensions is performed in step S5, which will be described later.

[0030] Next, a common material paste that will be the basis for the intermediate layer 30 is printed by screen printing on one surface of the fired body of the second ceramic layer 20 (step S3). The common material paste is a paste made by kneading alumina powder, a binder, and a solvent. The common material paste is printed to a thickness of, for example, 20 μm. After printing, the fired body of the second ceramic layer 20 on which the common material paste has been printed is degreased at a predetermined temperature.

[0031] The sintered body of the first ceramic layer 10 and the sintered body of the second ceramic layer 20 are arranged so as to face each other with the common material paste interposed therebetween, and a joining process is carried out to join the sintered bodies (step S4). In the joining process, the laminate in which the two sintered bodies are stacked with the common material paste interposed therebetween is subjected to common material joining by hot pressing from both sides along the stacking direction.

[0032] FIG. 4 is an explanatory diagram of a press jig TL used in the bonding process. FIG. 4 shows a schematic cross-sectional view of the press jig TL and the laminate 1A before hot pressing during the bonding process. As shown in FIG. 4, the laminate 1A is compressed along the stacking direction during hot pressing. In this embodiment, the press surfaces FC1 and FC2 that press the laminate 1A during hot pressing have a recessed center in the surface direction. Therefore, each layer forming the laminate 1A is compressed with a stronger force toward the periphery than toward the center in the surface direction. As a result, the porosity of each layer is greater toward the center and smaller toward the periphery. Note that FIG. 4 shows the arrangement of each part schematically, and does not accurately represent the dimensional ratio of each part. For example, the recession amount at the center of the press surfaces FC1 and FC2 is not limited to the ratio shown in FIG. 4.

[0033] 3, the laminate 1A is processed (step S5) into the shape of the holding device 1 shown in FIGS. 1 and 2, and the manufacturing flow for the holding device 1 is completed. In the processing of step S5, the layers forming the laminate 1A are processed so that their diameters and thicknesses become the same as those of the first ceramic layer 10 and the second ceramic layer 20, respectively. In the processing of step S5, the portions of the through holes 52 formed in the second ceramic layer 20 and the intermediate layer 30 of the laminate 1A shown in FIG. 4 are formed so as to communicate with the through holes 52 formed in the first ceramic layer 10 in the processing of step S1.

[0034] FIG. 5 is an explanatory diagram of the porosity of the first ceramic layer 10, the intermediate layer 30, and the second ceramic layer 20. FIG. 5 shows SEM (Scanning Electron Microscope) photographs enlarging the cross sections of the holding device 1 at three different locations in the planar direction. FIG. 5 shows cross sections at a central position PS0 through which the central axis OL1 passes, a position PS65 at 65% of the radius from the center, and a peripheral position PS90 at 90% of the radius from the center in the radial direction perpendicular to the stacking direction. The peripheral position PS90 can also be expressed as a position 10% closer to the center from the peripheral end face. As shown in the cross section of FIG. 5, in the intermediate layer 30, the central position PS0 had the most pores P, and the peripheral position PS90 had the fewest pores P. In other words, among the three positions, the central position PS0 had the largest porosity, and the peripheral position PS90 had the smallest porosity. Similarly to the intermediate layer 30, the first ceramic layer 10 and the second ceramic layer 20 also had the largest porosity at the central position PS0 and the smallest porosity at the peripheral position PS90 among the three positions. In this embodiment, the average porosity of the entire second ceramic layer 20 is 1% or less. The average porosity of the entire first ceramic layer 10 is 5% or less. The average porosity of the entire intermediate layer 30 is 10% or less. In particular, the average porosity of the peripheral portion of the intermediate layer 30 is 5% or less. If the average porosity of the peripheral portion of the intermediate layer 30 is similar to the average porosity of the first ceramic layer 10, leakage of inert gas to the outside through the intermediate layer 30 is suppressed.

[0035] As described above, the holding device 1 of this embodiment includes the first ceramic layer 10 made of ceramic, the disk-shaped chuck electrode 40 disposed inside the first ceramic layer 10, the plate-shaped second ceramic layer 20 formed of ceramic, the intermediate layer 30 disposed between the first ceramic layer 10 and the second ceramic layer 20, and the gas flow path 50. The porosity of the outer periphery of the intermediate layer 30 is smaller than the porosity of the central portion. In this embodiment, the porosity of the intermediate layer 30 is smaller at the outer periphery than at the central portion. That is, the outer periphery of the intermediate layer 30 is denser than the central portion. This prevents leakage of an inert gas or the like through the intermediate layer 30 to the outside when an inert gas is supplied between the wafer W-holding surface 21 and the wafer W through the gas flow path 50. As a result, the inert gas supplied to the gas flow path 50 is sufficiently delivered to the wafer W-holding surface 21, thereby uniformizing the in-plane temperature of the wafer W. Furthermore, the center of the intermediate layer 30 is compressed by atmospheric pressure, but because the porosity of the center is higher than that of the outer periphery, the center functions as a stress relief layer that relieves stress. In particular, the closer the gas flow channel 50 is formed to the center, the more the leakage of the inert gas is suppressed, and the better the center functions as a stress relief layer.

[0036] Furthermore, the intermediate layer 30 is formed so that its thickness t30 along the stacking direction is 50 μm or less. With this configuration, the thickness of the intermediate layer 30 is small, 50 μm or less, and therefore the inert gas supplied to the gas flow path 50 is prevented from leaking to the outside through the intermediate layer 30.

[0037] In particular, in this embodiment, the holding device 1 is formed so that the thickness t10u of the first ceramic layer 10 along the stacking direction from the surface of the chuck electrode 40 on the positive side of the Z axis to the intermediate layer 30 is smaller than the thickness t20 of the second ceramic layer 20 and greater than the thickness t30 of the intermediate layer 30. In this embodiment, the thickness t20 of the second ceramic layer 20 that holds the wafer W is increased, thereby improving the dechucking performance of the wafer W. On the other hand, the increased thickness t20 of the second ceramic layer 20 brings the intermediate layer 30 closer to the inlet of the gas flow path 50 (located on the negative side of the Z axis), which may increase leakage of the inert gas. However, in this embodiment, the porosity of the outer periphery of the intermediate layer 30 is smaller than the porosity of the center portion, thereby suppressing leakage of the inert gas and improving the dechucking performance of the wafer W.

[0038] Furthermore, the porosity of the second ceramic layer 20 in this embodiment is smaller than the porosity of the first ceramic layer 10. In this embodiment, the porosity of the second ceramic layer 20, where the mounting surface 21 that holds the wafer W is exposed, is smaller than the porosity of the first ceramic layer 10. As a result, the voltage resistance of the holding device 1 is improved, and the particle resistance of the second ceramic layer 20 is improved.

[0039] In addition, the intermediate layer 30 in this embodiment is made of alumina, a ceramic material. In this embodiment, in addition to the first ceramic layer 10 and the second ceramic layer 20, the intermediate layer 30 is also made of ceramic. Therefore, the entire holding device 1 is less susceptible to deterioration due to plasma irradiation.

[0040] In addition, the main component of the intermediate layer 30 in this embodiment is alumina. In this embodiment, the three layers, i.e., the first ceramic layer 10, the intermediate layer 30, and the second ceramic layer 20, are formed using the same ceramic as the main component. Therefore, the compositions of the materials forming these three layers are very similar, which reduces the difference in thermal expansion when the three layers are sintered together.

[0041] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0042] <Variation 1> In the above embodiment, an example of the holding device 1 that holds a wafer W as an object has been described. However, the holding device 1 is deformable in a plane direction perpendicular to the stacking direction within a range in which the porosity of the peripheral portion of the intermediate layer 30 is smaller than the porosity of the central portion. For example, unlike the SEM photograph shown in FIG. 5, the porosity of the central portion of the first ceramic layer 10 and the second ceramic layer 20 may be smaller than the porosity of the peripheral portion. Furthermore, the porosity of the second ceramic layer 20 may be equal to or greater than the porosity of the first ceramic layer 10.

[0043] The thickness t10u of the first ceramic layer 10 may be less than 1 μm or greater than 150 μm. The thickness t30 of the intermediate layer 30 may be less than 1 μm or greater than 50 μm. The thickness t20 of the second ceramic layer 20 may be less than 150 μm or greater than 350 μm. The diameter dimensions in the planar direction of the first ceramic layer 10, the intermediate layer 30, and the second ceramic layer 20 are also variable, similar to the thicknesses. The thickness t10u of the first ceramic layer 10 may be greater than or equal to the thickness t20 of the second ceramic layer 20, or less than or equal to the thickness t30 of the intermediate layer 30.

[0044] In the above embodiment, the first ceramic layer 10, the second ceramic layer 20, and the intermediate layer 30 are formed of ceramics containing alumina as a main component. However, the materials forming the first ceramic layer 10, the second ceramic layer 20, and the intermediate layer 30 can be modified. For example, the first ceramic layer 10, the second ceramic layer 20, and the intermediate layer 30 may each be formed of a different ceramic as a main component. The first ceramic layer 10 and the second ceramic layer 20 may be formed of ceramic, and the intermediate layer 30 may not contain ceramic. The first ceramic layer 10, the second ceramic layer 20, and the intermediate layer 30 may be formed of ceramics containing aluminum nitride (AlN) as a main component. It is more preferable that the first ceramic layer 10, the second ceramic layer 20, and the intermediate layer 30 contain at least 99 wt% of the same ceramic as a main component.

[0045] <Variation 2> 3 is an example of a method for manufacturing an intermediate layer 30 having a lower porosity in the center than in the outer periphery, and the holding device 1 may be manufactured by a different manufacturing method. The manufacturing method of the above embodiment can also be rephrased as follows.

[0046] A method for manufacturing a holding device, comprising: a step of laminating and disposing a bonding layer on which an adhesive is printed between a first ceramic layer formed of ceramic and a second ceramic layer formed of ceramic and different from the first ceramic layer; a bonding step of thermally compressing a laminate of the first ceramic layer, the bonding layer, and the second ceramic layer in a lamination direction; Run The manufacturing method is characterized in that in the joining step, a force compressing the outer periphery of the laminate in a direction perpendicular to the stacking direction is greater than a force compressing the center of the laminate.

[0047] In other words, in the manufacturing method of the above aspect, the method of controlling the compression force in the joining process does not require the use of concave press surfaces FC1, FC as in the above embodiment, and the compression force may be controlled by other methods.

[0048] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0049] The present invention can also be realized in the following forms. [Application example 1] A holding device for holding an object, a first ceramic layer formed of ceramic; a plate-shaped second ceramic layer formed of ceramic and disposed on the first ceramic layer; an intermediate layer disposed between the first ceramic layer and the second ceramic layer; a gas flow path passing through the first ceramic layer, the intermediate layer, and the second ceramic layer; Equipped with the intermediate layer has an outer peripheral portion located outside and a central portion located inside in a direction perpendicular to a stacking direction of the first ceramic layer, the intermediate layer, and the second ceramic layer, The porosity of the outer periphery is smaller than the porosity of the central portion. A holding device characterized by: [Application example 2] The holding device according to Application Example 1, In the stacking direction, the thickness of the intermediate layer is 50 micrometers (μm) or less. A holding device characterized by: [Application example 3] The holding device according to Application Example 1 or Application Example 2, further comprising: a plate-shaped electrode disposed inside the first ceramic layer; a thickness of a portion of the first ceramic layer between the electrode and the intermediate layer in the stacking direction is smaller than a thickness of the second ceramic layer and larger than a thickness of the intermediate layer; A holding device characterized by: [Application example 4] The holding device according to any one of Application Examples 1 to 3, The porosity of the second ceramic layer is smaller than the porosity of the first ceramic layer. A holding device characterized by: [Application example 5] The holding device according to any one of Application Examples 1 to 4, The intermediate layer is made of ceramic. A holding device characterized by: [Application Example 6] The holding device according to any one of Application Examples 1 to 5, The first ceramic layer, the intermediate layer, and the second ceramic layer each have the same main component. A holding device characterized by: [Explanation of symbols]

[0050] 1...Holding device 1A...Laminate 10...First ceramic layer 11...Top of the first ceramic layer 12...Lower part of the first ceramic layer 13...Heater electrode 14...Power lines 20...Second ceramic layer 21...Placement surface 30...Middle class 40...Chuck electrode 50...Gas flow path 51...Communication hole 52...Through hole 53...Tunnel CS...Cartesian coordinate system FC1, FC2...Press side OL1…Center axis P…Pore TL...Press jig W...wafer (object)

Claims

1. A holding device for holding an object, a first ceramic layer formed of ceramic; a plate-shaped second ceramic layer formed of ceramic and disposed on the first ceramic layer; an intermediate layer disposed between the first ceramic layer and the second ceramic layer; a gas flow path passing through the first ceramic layer, the intermediate layer, and the second ceramic layer; Equipped with the intermediate layer has an outer peripheral portion located outside and a central portion located inside in a direction perpendicular to a stacking direction of the first ceramic layer, the intermediate layer, and the second ceramic layer, The porosity of the outer periphery is smaller than the porosity of the central portion. A holding device characterized by:

2. 2. The holding device of claim 1, In the stacking direction, the thickness of the intermediate layer is 50 micrometers (μm) or less. A holding device characterized by:

3. 10. The holding device of claim 1, further comprising: a plate-shaped electrode disposed inside the first ceramic layer; a thickness of a portion of the first ceramic layer between the electrode and the intermediate layer in the stacking direction is smaller than a thickness of the second ceramic layer and larger than a thickness of the intermediate layer; A holding device characterized by:

4. 2. The holding device of claim 1, the porosity of the second ceramic layer is less than the porosity of the first ceramic layer; A holding device characterized by:

5. A holding device according to any one of claims 1 to 4, The intermediate layer is made of ceramic. A holding device characterized by:

6. 6. The holding device according to claim 5, the first ceramic layer, the intermediate layer, and the second ceramic layer each have the same main component; A holding device characterized by:

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